1. Field of the Invention
The present invention relates to an optical recording and replay device which performs recording and replay of data by illuminating an optical disk recording substrate with a light beam. In particular, the present invention relates to an optical disk device which performs an auto gain control (AGC) process on servo signals which perform illuminating control of the spot of the light beam on the recording surface of the optical disk.
2. Description of the Related Art
An example of a known device of this type of optical disk device is shown in FIG. 2. In FIG. 2, a spindle motor 2 rotates an optical disk 1. An objective lens 3 causes focusing of a light beam (laser light) which is generated by a laser 10. The optical disk 1 is illuminated by this laser beam. An optical detector 4 detects the amount of reflected light of the light beam illuminating the optical disk 1.
The objective lens 3 is movable in a direction to follow the tracks (namely, a parallel direction with respect to the recording surface of the optical disk), or a direction transverse to the tracks of the optical disk 1, by an actuator 5. Moreover, the objective lens 3 is movable in a direction perpendicular to the recording surface of the optical disk 1 by an actuator 6.
A recording signal processing unit 7 processes the data which is to be recorded on the optical disk 1. The laser 10 is controlled by a laser control unit 8 and a laser drive unit 9. Moreover, an analog divider 11 performs analog division based on the difference signal (the tracking error signal TE, mentioned later) and the sum signal (entire amount of reflected light) of the reflected light detected by the optical detector 4. The analog divider 14 performs analog division based on the difference signal (the tracking error signal TE, mentioned later) and the sum signal of the reflected light detected by the optical detector 4.
In this manner, a prior art optical disk device, with analog dividers 11, 14, provides a focus error signal FE and a track error signal TE as respective wave inputs, and in addition provides a total amount of light (sum signal) as a divider input.
Then, by the gain of a first servo loop consisting of the analog divider 11, servo processing unit 12, amplifier 13 and actuator 5, tracking control of the light beam with respect to the track of the optical disk 1 is performed on the one hand, and by the gain of a second servo loop consisting of the analog divider 14, servo processing unit 15, amplifier 16 and actuator 6, focus control is performed which controls the focal position of the light beam with respect to the recording surface of the optical disk 1.
In this manner, in a prior art optical disk device, the gain of the autofocus servo or tracking servo or the like servo loops are set by an analog divider, independently of the amount of reflected light. However, in optical disks, because the reflectivity of the recording surface from each manufacturer is generally different, when the focus control or tracking control of each optical disk is performed by the servo loops of the prior art devices, scattering of the loop gain occurs due to scattering of the amount of reflected light. Thus, the problem existed that oscillation sometimes occurred in the servo loops.
Moreover, in such a prior art device, the responsiveness to changes in the amount of light was poor, and at the moment of beginning or ending data recording, gain errors arose due to not being able to follow the changes of the amount of light. A problem also existed that the servos did not operate stably. Furthermore, because an analog divider was used, there was a problem that offset voltages tended to arise due to the effects of temperature or power supply changes.